Hi,

[auto build test WARNING on drm-intel/for-linux-next]
[also build test WARNING on next-20160420]
[cannot apply to v4.6-rc4]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Matt-Roper/Pre-calculate-SKL-style-atomic-watermarks/20160420-102913
base:   git://anongit.freedesktop.org/drm-intel for-linux-next
config: x86_64-randconfig-n0-04210735 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   drivers/gpu/drm/i915/intel_pm.c: In function 'skl_compute_wm':
>> drivers/gpu/drm/i915/intel_pm.c:2903:5: warning: 'num_active' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if (num_active == 1)
        ^
   drivers/gpu/drm/i915/intel_pm.c:3057:6: note: 'num_active' was declared here
     int num_active;
         ^

vim +/num_active +2903 drivers/gpu/drm/i915/intel_pm.c

000bcc21 Matt Roper     2016-04-19  2887  	if (!intel_state->active_pipe_changes) {
000bcc21 Matt Roper     2016-04-19  2888  		*alloc = dev_priv->wm.skl_hw.ddb.pipe[pipe];
000bcc21 Matt Roper     2016-04-19  2889  		*num_active = hweight32(dev_priv->active_crtcs);
000bcc21 Matt Roper     2016-04-19  2890  		return;
000bcc21 Matt Roper     2016-04-19  2891  	}
000bcc21 Matt Roper     2016-04-19  2892  
000bcc21 Matt Roper     2016-04-19  2893  	*num_active = hweight32(intel_state->active_crtcs);
000bcc21 Matt Roper     2016-04-19  2894  	nth_active_pipe = hweight32(intel_state->active_crtcs &
000bcc21 Matt Roper     2016-04-19  2895  				    (drm_crtc_mask(for_crtc) - 1));
000bcc21 Matt Roper     2016-04-19  2896  	pipe_size = ddb_size / hweight32(intel_state->active_crtcs);
000bcc21 Matt Roper     2016-04-19  2897  	alloc->start = nth_active_pipe * ddb_size / *num_active;
000bcc21 Matt Roper     2016-04-19  2898  	alloc->end = alloc->start + pipe_size;
b9cec075 Damien Lespiau 2014-11-04  2899  }
b9cec075 Damien Lespiau 2014-11-04  2900  
000bcc21 Matt Roper     2016-04-19  2901  static unsigned int skl_cursor_allocation(int num_active)
b9cec075 Damien Lespiau 2014-11-04  2902  {
000bcc21 Matt Roper     2016-04-19 @2903  	if (num_active == 1)
b9cec075 Damien Lespiau 2014-11-04  2904  		return 32;
b9cec075 Damien Lespiau 2014-11-04  2905  
b9cec075 Damien Lespiau 2014-11-04  2906  	return 8;
b9cec075 Damien Lespiau 2014-11-04  2907  }
b9cec075 Damien Lespiau 2014-11-04  2908  
a269c583 Damien Lespiau 2014-11-04  2909  static void skl_ddb_entry_init_from_hw(struct skl_ddb_entry *entry, u32 reg)
a269c583 Damien Lespiau 2014-11-04  2910  {
a269c583 Damien Lespiau 2014-11-04  2911  	entry->start = reg & 0x3ff;

:::::: The code at line 2903 was first introduced by commit
:::::: 000bcc2112fef02e609ad72f6ae43fd027ce8564 drm/i915/gen9: Allow skl_allocate_pipe_ddb() to operate on in-flight state (v2)

:::::: TO: Matt Roper <matthew.d.roper@intel.com>
:::::: CC: 0day robot <fengguang.wu@intel.com>

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